Reproductive parasitism

Many arthropods (insects, mites, spiders etc.) are home to microorganisms that live inside them in close association as endosymbionts. Often, these microbes are inherited exclusively from mother to offspring. This means that endosymbionts finding themselves in a male host normally have no prospects of leaving descendants in the long run. However, some endosymbionts have evolved ways to overcome this problem: they manipulate the reproduction of their hosts to their own advantage, but to the hosts’ detriment. Some of these so-called reproductive parasites “simply” turn infected males into females (which then can pass on the infection). Others selectively kill their male hosts as embryos (“male-killing”) or render males conditionally sterile (“cytoplasmic incompatibility”).

Reproductive parasites are diverse and very common. The most famous is the alpha-proteobacterium Wolbachia, which alone probably infects more than 50% of all terrestrial arthropod species. In addition to acting as a reproductive parasite, Wolbachia also protects some of its host from pathogens or provide nutrients. Other bacteria known to engage in reproductive parasitism include Cardinium, Rickettsia, and Spiroplasma.

Mating couple of Hypolimnas bolina: This tropical butterfly is infected by at least two strains of Wolbachia.

We are interested in the distribution of reproductive parasites, how they spread within and among host species, how they evolve and how they affect the ecology and evolution of their hosts. Why is Wolbachia more common in some arthropod groups than in others? How do different reproductive parasites influence each others spread in a host population? How do reproductive parasites that distort the sex ratio basic evolutionary processes in their hosts? These and other questions are addressed through mathematical models and through surveys of natural arthropod populations.